Thermostatic overload relay



Filed Jan. '7, 1944 27 a 15 22 g 5H3 ,3 20 17 15 22 /5 53 U @YJ E WITN ESSE SZ INVENTOR George 6. flrmsimzzg.

aha/( AM M ATTORNEY Patented July 23, 1946 THERMOSTATIC OVERLOAD RELAY George G. Armstrong, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 7, 1944, Serial No. 517,307

8 Claims. 1

My invention relates to thermally operating electric apparatus in which a spring biased movable member is normally prevented from following its bias and is released electrically upon the occurrence of a given thermal condition. More particularly, this invention concerns overload relays and the like protective devices to be operated in response to the occurrence of a given load condition.

It is known to provide devices of this type with a low melting solder joint which holds a spring biased contact member in position as long as the temperature remains below the fusing value and becomes soft, thereby releasing the contact member, when this value is exceeded due to an undue increase in heating current. These devices are subject to change their operating characteristic due to oxidation of the solder and other ageing effects. More favorable in the latter respect are overload relays in which a heat-deformable thermostat is employed for actuating a ratchet or latch mechanism so as to release the spring biased contact member when heated beyond a maximum temperature corresponding to a rated overload current. of the latter type require considerably more space and are more complicated, or less accurate and usually more expensive to manufacture.

It is an object of my invention to provide a device which combines the advantages of the thermostatic type with those of the alloy or solder type. That is, it is intended by this invention to devise a thermal or overload relay of Very small dimensions and great accuracy and reliability that is free of the ageing effects of solder type relays.

Another object of my invention is to provide improved thermoresponsive latching or clutching means for relays or the like apparatus so as to obtain a release operation of high reliability and sensitivity by mechanical means of extremely small dimensions.

It is also an object to design a device of the type above referred to in such a manner that the releasable latching or clutching means act along the entire periphery of the movable member to be latched so as to be capable of exerting a considerable retaining force thereon, and it is further aimed at achieving this result while requiring only a slight movement of the clutch or latch means for elfecting the release of the movable member.

In order to achieve these and other objects which will become apparent from the following However, the known devices mostatic metal winding on a pin or shaft member so as to grip this member tightly when cold While loosening its grip when heated beyond a given extent.

According to another feature of the invention, a helical bimetal winding or spring is provided or connected with a detent or latch member for retaining a spring biased switch member, and is seated on a stationary shaft structure so as to exert a clutching grip on the shaft when affected by the spring bias and in cold condition, while relaxing its grip when either heated or caused to perform an unwinding motion, the latter way of release operation being used for resetting the relay.

A further feature of the invention consists in providing a shaft structure of the abovementioned type which is composed of a slotted sleeve and an inner conical post so as to permit varying the diameter of the sleeve in order to calibrate the release mechanism.

According to still another feature, my invention provides a single insulating body for accommodating all individual parts, including the above-mentioned mechanism as well as the contact and heater elements of the relay so as to obtain a compact device of simple design and small compass.

An embodiment in accordance with the abovementioned objects and features of the invention is illustrated in the drawing, in which:

Figure 1 is a top View; Fig. 2 a lateral view; and Fig. 3 a front View of a thermostatic overload relay;

Fig. 4 is a cross-section taken along the plane indicated in Fig. 2 by the dot-and-dash line marked IV-IV;

Fig. 5 is an axial section along the plane denoted in Fig. 3 by the dot-and-dash line marked VV; and

Fig. '6 is an exploded View of a number of individual parts which, when properly assembled,

description, my invention requires a helical ther- 88 form the thermostatic latching or clutching device of the overload relay.

The illustrated device has an insulating body I with two raised portions 2 and 3. An axial cavity 4 is provided in portion 3 of the insulating body, while the portion 2 has a bore extending substantially in a tangential direction to the cavity 4. The bore and the cavity are in communication with each other (Figs. 4 and 5).

Two openings 5 and 5 are provided in body I for fastening it to a suitable support. A plunger 1 is arranged in the bore of body i. This plunger carries a push button at its upper end and ha a radially restricted portion at 9. A helical compression spring placed in the bore underneath the plunger tends to move the plunger in the outward direction relative to the insulating body.

A contact bridge H is slidably mounted on the plunger 1 underneath the push button 8, so as to be axially displaceable relative to the plunger. A washer or projection 32 firmly connected with the plunger 1 forms an abutment for the contact bridge I I, and a sprin I2 is provided for biasing the bridge I I against the abutment 32.

Two contact terminals l3 and [4, each provided with a binding screw, are mounted on the top surface of the raised base portion 2. These two terminals form stationary contacts which are bridged by the contact member I I when the push button 8 is in depressed position.

A helical bimetal winding [5, which has an extended end portion IS in engagement with the restricted portion 9 of the plunger, serves to latch the plunger in its depressed position. The winding is relatively tightly seated on a slotted sleeve i! which, in turn, is mounted On a conical post [8. One end E9 of this post is riveted to the angular poition 22 of a contact terminal 23. The other end 20 of the post it! is threaded and carries an adjusting nut 2 i. When the parts l5, IT, l8, 2! and 22 are assembled as shown in Fig. 5, the nut -2I rests against a washer which, in turn, rests against the adjacent front surface of the slotted sleeve IT. The inner bore of the sleeve is tapered so that the diameter of the outer sleeve surface engaged by the inner surface of the bimetal winding l5, depends on the axial position of the sleeve relative to the conical post i8. This position can be changed with the eifect of widening the sleeve ll by screwing the nut 21 tighter against the sleeve. Once properly adjusted, the nut 2i may be soldered to the threaded portion 28 of the post in order to secure the adjusted setting. Due to the frictional engagement between the sleeve H and the bimetal winding, the winding is prevented from rotating relative to the sleeve in a direction which would tend to wind the bimetal more tightly about the sleeve. However, when the end It is moved in the opposite, i. e. unwinding, direction, the turns of the bimetal winding are loosened sufiiciently to permit a rotation of the winding. The winding is surrounded b a helical heater 29.

The above-mentioned terminal 23 is mounted on the top face of the base portion 3 and has a binding screw 25 for fastening one end 3| of the heater winding 29 thereto. A second terminal 2 also mounted on the base portion 3, has a binding screw 26 for fastening the other end 36 of the heater. The two terminals 23 and 24 have additional binding screws 21 and 28, respectively, for connecting thereto the leads of the electrical circuit to be controlled by the relay. When in operation, th current flowing from terminal 23 through the heater 2! to the terminal 26 has the effect of heating the bimetal winding Hi. When the temperature of winding i5 rises beyond a given value due to the occurrence and persistence v of an overload, the winding expands its turns and loosens from the sleeve l! to a sufiicient extent to permit a rotation of the bimetal winding in either direction,

The relay operates in the following manner. The illustration shows the control contacts 6 I, I3 and M in interrupted condition with the actuating plunger 1 in its uppermost position. When the push button 8 is depressed, the bridge H closes the contact between terminals l3 and M (Fig. 3). This has the efiect of controlling a contactor (not illustrated) to close the main circuit to be controlled extending over the terminals 23 and 24 and the heater 29. When pushing the button 8, the end [6 of the bimetal winding [5 is moved downwardly (Fig. 4) in the unwinding direction. Hence the bimetal winding is capable of rotation relative to the shaft structure. After the lowermost position of the plunger 1 is reached and the spring l0 compressed, the bimetal winding l5 grips the sleeve I1 and retains the plunger 1 in the depressed position. As long as the load current remains below a Certain magnitude, the heat developed by heater 29 is insufficient to loosen the frictional grip of the bimetal winding. When an overload occurs and persists for a sufiicient time to overheat the bimetal, the loosening of the bimetallic winding releases it for rotation, so that now the spring I0 is capable of moving the plunger 1 and the contact bridge into the illustrated opening position. This causes an interruption of the main current through winding 29 so that the thermostatic mechanism is permitted to cool. After expiration of the cooling period, the mechanism is again in condition for returning the plunger into contact closing position.

It will be apparent from the above-described embodiment in conjunction with the drawing that the releasable latching or clutching device of the relay is of extremely small dimensions, although the holding force developed by the thermostatic winding is very large due to the fact that it acts along the entire periphery of the clutching device and along any desired number of turns. It will also be apparent that the tripping value of the load current can be readily adjusted with the aid of the nut 2|.

While I have illustrated an embodiment in which a slotted and expansible sleeve is used in order to improve the adjustability of the thermostatic device, it is also possible to provide the helical thermostat winding with a slightly tapered inner bore and to place it directly on a conical post, the operation and adjustability of the device remaining substantially as described in the foregoing.

It should be understood that while I have illustrated a single embodiment of my invention, the essential elements of the releasable thermostatic device may be associated with electric devices different from the illustrated overload relay. In view of such modifications which will be obvious to those skilled in the art upon studying my present disclosure, 1' wish this specification to be understood as illustrative and not in a limiting sense.

I claim as my invention:

1. A relay comprising a shaft member and a helical spring member revolvable relative to each other, said spring member being coaxially seated on said shaft to grip it normally in order to prevent relative revolution in one direction, a movable and spring biased relay structure connected with one of said members so as to be retained, when in proper position, in opposition to its spring bias, and electric means for causing said spring member to expand radially in order to release said shaft so as to permit said structure to move under its bias.

2. A relay comprising a stationary shaft, a helical clutch spring coaxially seated on said shaft so as to be revolvable in one direction while gripping the shaft so as to be normally prevented from revolving in the other direction, a movable and spring biased structure connected to said clutch spring so as to be retained, when in proper position, against the action of its spring bias, and electric means for causing said clutch spring to expand radially in order to release said shaft so as to permit said structure to move under its bias.

3. A relay comprising a shaft member and a helical thermostatic member revolvable relative to each other, said thermostatic member being coaxially seated on said shaft so as to grip it in order to prevent relative revolution in one direction, a movable and spring biased relay structure connected with one of said members so as to be retained, when in proper position, in opposition to its spring bias, and electric heating means associated with said thermostatic member for causing it to expand radially in order to loosen its grip on said shaft member upon occurrence of given temperature conditions.

4. A relay comprising a stationary shaft, a helical bimetal strip coaxially seated on said shaft so as to be revolvable in one direction while gripping the shaft so as to be normally prevented from revolving in the other direction, a movable and spring biased structure connected to said strip so as to be retained, when in proper position, against the action of its spring bias, and electric heating means associated with said strip for causing it to expand radially in order to loosen its grip on said shaft member upon occurrence of given temperature conditions.

5. A relay comprising a stationary shaft, a helical bimetal strip coaxially seated on said shaft so as to be revolvable in one direction while gripping the shaft so as to be normally prevented from revolving in the other direction, a movable and spring biased structure connected to said strip so as to be retained, when in proper position, against the action of its spring bias, electric heating means associated with said strip for causing it to expand radially in order to loosen its grip on said shaft member upon occurrence of given temperature conditions, and reset means associated with said structure for moving it against its bias so as to revolve said strip in its unwinding direction.

6. A relay mechanism comprising a conical post, an expansible sleeve member disposed on said post for adjusting the sleeve diameter in accordance with the relative axial position of sleeve and post, a helical clutch member coaxially seated on said sleeve to grip it so as to be normally revolvable only in its unwinding direction relative to said sleeve, a movable and spring biased relay structure connected with one of said members so as to be retained, when in proper position, in opposition to its spring bias, and electric means for causing said helical clutch member to expand radially in order to release said shaft so as to permit said structure to move under its bias.

7. A relay mechanism comprising a stationary conical post, a slotted 'expansible sleeve having a conical bore and being firmly seated on said post in a position corresponding to a desired outer sleeve diameter, a helical bimetal coaxially seated on said sleeve to grip it so as to be normally revolvable only in its unwinding direction relative to said sleeve, a movable and spring biased relay structure connected with one end of said bimetal so as to be retained, when in proper position, against the action of its spring bias, and electric heating means associated with said bimetal for causing it to expand radially in order to loosen its grip on said sleeve upon occurrence of a predetermined electric condition.

8. A relay comprising a stationary shaft, a helical bimetal strip coaxially seated on said shaft so as to be revolvable in one direction while gripping the shaft so as to be normally prevented from revolving in the other direction, a movable and spring biased structure connected to said strip so as to be retained, when in proper position, against the action of its spring bias, and an electric heating winding surrounding said helical strip in order to cause it to expand radially so as to loosen its grip on said shaft member upon occurrence of an electric overload.

GEORGE C. ARMSTRONG. 

